Good grief! I'm sorry to hear about what you've been going through. Have you considered consulting with a behaviorist? That would be the first thing I might do. Maybe I'd talk to my vet first, then a behaviorist.
Some dogs naturally have high prey drives, but it sounds as if your girl just went nuts for some reason unknown to you.
My girl has a very high prey drive. I adopted her through rescue, but the first woman who tried to adopt her sadly had to return her b/c she had some cats and also fed some strays and Tae went nuts on two occasions (within a week) and killed two of the strays. She goes bonkers now over cats, but we haven't had any close enounters, thank gosh, and hopefully we never will.
Taebo -- Flashy Fawn Devil, born 12/02/02, adopted 01/10/04